In controlled environments, such as airplanes, submarines, or spacecraft, oxygen is necessary to maintain a habitable environment or provide emergency life support. This oxygen can be stored under high pressures ranging from about 1,000 pounds per square inch (psi) to about 6,000 psi. For example, in commercial airplanes, the oxygen is typically stored at pressures exceeding about 1,850 psi. As a result, oxygen must be either produced at a high pressure or compressed prior to storage. The production of this high pressure oxygen generally requires the use of extensive equipment such as compressors and pressure control devices.
One common high pressure oxygen preparation technique comprises introducing water to a pump which increases the pressure of the water to between 1,500 and 2,500 psi. The pressurized water is then introduced to an electrolysis cell comprising an anode, a cathode, an ion exchange membrane disposed therebetween, an anode chamber, and a cathode chamber. There are about 1.4 (theoretical) volts of electricity applied to the electrolysis cell such that the high pressure water is electrolyzed to high pressure hydrogen ions and oxygen at the anode. The high pressure hydrogen ions flow across the ion exchange membrane to the cathode due to the conductive path formed by the potential gradient across the ion exchange membrane. At the cathode, the hydrogen ions form high pressure molecular hydrogen, while the high pressure oxygen exits the electrolysis cell through the anode chamber.
Due to the state of electrolyzer art and the limited structural integrity of the ion exchange membrane, the pressure gradient across the ion exchange membrane should not exceed about 200 psi. Pressure gradients greater than about 200 psi induce ion exchange membrane failure by causing the extrusion of the membrane into the cathode chamber. As a result, the cathode chamber pressure must be maintained within about 200 psi of the water pressure entering the electrolysis cell. Maintenance of the pressure within the cathode chamber requires the employment of compressors and/or pressure control devices. Therefore, compressors and pressure control devices are needed to maintain the pressure of both the feed water and the cathode chamber. Furthermore, high pressure tolerant equipment is required for the entire electrolysis cell.
Another method of producing high pressure oxygen comprises introducing water to the anode chamber at ambient pressure. The water is electrolyzed at the anode to hydrogen ions and oxygen. The hydrogen ions flow across the ion exchange membrane to the cathode where they are formed into molecular hydrogen. The molecular hydrogen exits the electrolyzer through the cathode chamber. Meanwhile, the oxygen exits the anode chamber and is introduced to a compressor which pressurizes the oxygen to between 1,500 and 2,000 psi. Although this system eliminates the ion exchange membrane extrusion problem, it still requires additional equipment, including the compressor and pressure control devices.
What is needed in the art is a simplified system and method for producing high pressure oxygen capable utilizing ambient or low pressure water.